In vehicles, a transmission is arranged between the internal combustion engine and driving wheels. According to the transmission, the driving force of the driving wheels and the running velocity are changed in accordance with the running conditions of the vehicle which change in a wide range, thereby making the performance of the internal combustion engine sufficiently effective. In a known continuous variable transmission in which a pulley has a fixed pulley member fixed to a rotary shaft and a movable pulley member attached to the rotary shaft so as to be movable toward and away from the fixed pulley member, and the width of a groove formed between the pulley members is increased and decreased to thereby respectively decrease and increase the rotational radius of a belt which is reeved to the pulley, whereby motive power is transferred, and the belt ratio is changed. Such a continuous variable transmission has been disclosed in, for instance, JP-A-57-186656, JP-A-59-43249, JP-A-59-77159, and JP-A-61-233256.
The applicant of the present invention has already developed a method of controlling a continuous variable transmission, in which a throttle opening degree detection signal, a vehicle velocity detection signal, and a rotational speed limiting command at a shift position are input to a control unit, an optimum target engine rotational speed is determined, and a speed change control is performed (JP-A-64-44346).
In the conventional control apparatus, when a target value of the speed change control is set, upper and lower limit values are set on the basis of the throttle opening degree, vehicle velocity, shift position such as D, L.sub.1, L.sub.2, a power mode option signal, or the like. However, there are inconveniences in that the vehicle running state which is desired by the driver, for instance, a running state adapted to a mountain road, a city street, a highway, a downtown road, or the like cannot be set and it is impossible to assure various characteristics such as economical performance of the vehicle, silence, acceleration response speed, engine braking effect, and the like.
In the known transmission control system, since the running state is selected on the basis of only the detection signal of the shift position, there are inconveniences such that speed change characteristics which satisfy the driver cannot be obtained and, further, it is necessary to widely set a degree of selection.
It is therefore an object of the present invention to provide a continuous variable transmission control apparatus including a control unit for receiving a throttle opening degree detection signal and a vehicle velocity detection signal, for determining an optimum target engine rotational speed from a first target engine rotational speed based on the throttle opening degree detection signal and from a second target engine rotational speed based on the vehicle velocity detection signal, for setting upper and lower limit values for the optimum target engine rotational speed in accordance with predetermined conditions, for obtaining a final target engine rotational speed, and for executing a speed change control so as to assure that desired operating characteristics are adapted to the vehicle state. The desired operating characteristics can be assured by the predetermined conditions and the operating performance, and characteristics such as economical performance, accelerating performance, engine braking effect, or the like can be freely selected.
To accomplish the above object, according to the invention, in an apparatus for controlling a continuous variable transmission including a fixed pulley member and a movable pulley member attached to the fixed pulley member so as to be movable toward and away from the fixed pulley member, the width of a groove between both of the pulley members is decreased and increased to thereby respectively increase and decrease the rotational radius of a belt which is reeved between both of the pulley members, and speed change control is executed so as to change the belt ratio. A control unit is provided for receiving throttle opening degree and vehicle velocity detection signals, for determining an optimum target engine rotational speed from a first target engine rotational speed based on the throttle opening degree detection signal and from a second target engine rotational speed based on the vehicle velocity detection signal, for setting upper and lower limit values of the optimum target engine rotational speed in accordance with predetermined conditions, for obtaining a final target engine rotational speed, and for executing speed change control so as to assure desired operating characteristics adapted to the vehicle running state.
When the vehicle is driven, the throttle opening degree and vehicle velocity detection signals are input to the control unit to thereby decide the optimum target engine rotational speed. The upper and lower limit values of the optimum target engine rotational speed are set in accordance with predetermined conditions, and the final target engine rotational speed is obtained.